Bootable El-Torito CD with GRUB Legacy: Difference between revisions

You will need the following:

* [[mkisofs]], which is in fact superseeded by [[genisoimage]].

* The El-Torito GRUB Legacy stage2 file, called <tt>stage2_eltorito</tt>.

 

 

 

 

We need a place to store the files on the CD image:

 

cd # Go to your home directory.

mkdir -p isofiles/boot/grub

 

You now created an <tt>isofiles</tt> directory in your home folder and a <tt>boot/grub</tt> sub-folder inside that. We need the stage2 file. It is installed from the grub package. Just copy it:

 

cp /usr/lib/grub/i386-pc/stage2_eltorito ~/isofiles/boot/grub/

 

=== Windows ===

 

<!-- Not really Bash, it's Grub scripting, but lang="bash" makes nice syntax highlighting. -->

default 0

#timeout 30

title My kernel

kernel /boot/kernel-file # Edit it to the filename of your kernel.

 

In GRUB there's a concept called root. It's the disk drive or partition where you access the files, like the kernel image and modules. When booting from CD using <tt>stage2_eltorito</tt> you don't need to set the root as it is already set to "<tt>(cd)</tt>".

In the following I use the command <tt>genisoimage</tt>, but you can change it to <tt>mkisofs</tt> if that is what its called on your system. Open a command prompt/terminal and go to where the <tt>isofiles</tt> folder is located. It is your home directory on Ubuntu. Issue the command:

 

genisoimage -R -b boot/grub/stage2_eltorito -no-emul-boot -boot-load-size 4

-boot-info-table -o bootable.iso isofiles

 

Now you have a file called <tt>bootable.iso</tt>. Test it using your favourite emulator or burn it to a CD and test on a real computer. I will just explain the command line arguments we used for genisoimage:

=== Give it a label ===

 

 

=== Make it be quiet ===

You don't want to copy those files around in order to create the .iso image. Just use the '''-graft-points''' argument, like this:

 

genisoimage -graft-points # ...other arguments here...

boot/my-kernel.elf=build/my-kernel.elf

boot/grub/stage2_eltorito=thirdparty/grub/stage2_eltorito

modules/=build/modules/

 

You can use both files and folders together with the -graft-points argument.

If you don't find a solution to your problem below, please ask in [http://forum.osdev.org/ the forums].

 

 

The output of mkisofs looks like this:

</pre>

 

 

 

=== I get a permission denied error in Linux ===

The problem is that the -boot-info-table command line argument patches the boot file to include information about the CD, but the boot file is not writable by genisoimage. GRUB needs the boot file to be patched in order to access the CD properly. The solution is to make it writable, like this:

 

chown myself isofiles/boot/grub/stage2_eltorito # Make sure you are the owner of the file. Replace "myself"

# with your username. Maybe you need to use sudo.

chmod u+w isofiles/boot/grub/stage2_eltorito # Make the file writable for the owner of the file (you).

 

== See Also ==

* [[mkisofs]]

* [[Bootable CD]] - using floppy disk emulation

=== External Links ===

* [http://www.geocities.com/imulgrew/grub_files.tar.gz Package containing the GRUB stages] (including <tt>stage2_eltorito</tt>)

* [ftp://alpha.gnu.org/gnu/grub/grub-0.97.tar.gz Source for GRUB Legacy] to build it yourself

[[Category:Tutorials]]

[[Category:Bootloaders]]